Patent GB-544934-A (GB)
Title: Improved machine tool for cutting gears having curved teeth
IPC: B23F9/10
Filed: 1941-03-28
Abstract: 544,934. Gear-cutting. CRAVEN BROS., (MANCHESTER), Ltd., and OWEN, W. March 28, 1941, Nos. 4226/41, and 2172/42. [Class 83 (iii)] In a method of and apparatus for cutting a pair of tapered gears by continuous generation by a face mill cutter, one of the gears is cut on both concave and convex flanks by cutters arranged at the same radius in the head having a known eccentricity from the basic crown wheel axis while the other gear has its convex and concave flanks cut by cutters arranged at different radii and eccentricity in order to produce gears having a contact zone at a preselected point along the teeth. Thus if the contact zone is to be near the mid point X, Fig. 2, of a tooth then all the flanks of the gear member are cut by cutters moving along the arc FF about a centre C arranged at a distance E from the basic crown wheel centre O. It is seen that the convex flanks of the mating gear require to be cut with cutters moving on an arc F 1 , F, having a centre C, lying on the line CX, and having an eccentricity E 1 . Similarly for the concave flanks of the mating gear the cutters move along an arc F 2 , F 2 , having a centre C, whose eccentricity is E,. Similar considerations apply if the contact zone is to be localized at either of the ends X 1 , X, of the teeth. Thus if a crown wheel and pinion are to be cut with contact localised at X 1 , Fig. 3, the crown wheel is first cut with all the cutters set at radius CX 1  with eccentricity E 3 . The cutters are now set to a radius C 3 X 1  and all flanks of the pinion cut to a curvature X 1 F 1 . This curvature is correct only for the convex flank. The convex flank cutters are now removed from the head and the concave flanks recut to the curvature X 1 F 2  with the cutter centre at C 4 . Thus any type of contact can be obtained by moving the cutter centre along one of the lines CX, CX 1 , CX 2 , Fig. 6, with appropriate radial adjustment of the cutters in the head. The latter adjustment may be obtained by locating the cutter in a head similar to that described in Specification 537,399. To adjust the cutter centre along the required line it is moved about the corresponding one of the centres N, N 1 , N 2 , Fig. 6. The cutter head a is mounted in a member b adjustable in a drum d to which generating feed is imparted by worm gearing e. The member b is adjusted to vary the eccentricity of the cutter head centre C and secured in position by bolts h the adjustment being indicated by scales g. The member b has sets of holes N, N 1 , N 2  one set for cutting gears of each hand, these holes aligning in the central position of the member b with similar holes in an adjustable plate j. In operation, for full length tooth contact the cutter head is placed at the required eccentricity with the member b in a central position as indicated by the similar readings of the two scales g. If the localised contact is required one of the gears is first cut as above with member b in its central position. For cutting the second gear a pin is placed in one of the holes N ... N 2  and the members b pivoted on the plate j to an extent determined by gauging abutments r, s. The cutters are adjusted in the head and the second gear then generated. This forms one set of flanks to the correct curvature. To reform the other flanks the member b is swivelled in the opposite direction and the radii of the cutters for these flanks readjusted, the other cutters being removed.